Understanding Enzyme Inhibition in Biochemistry

undefined
 
BIOCHEMISTY
 
BINITA RANI
ASSOCIATE PROFESSOR (DAIRY CHEMISTRY)
FACULTY OF DAIRY TECHNOLOGY
S.G.I.D.T., BVC CAMPUS,
P.O.- BVC, DIST.-PATNA-800014
 
Course No.-DTC-111,    Credit Hours – 2 (1+1)
 
ENZYME INHIBITION
 
Inhibitors
 are molecules that => resemble the
substrate(s) 
or 
product(s) 
and 
bind to => 
active site
 =>
thus => they 
interfere with catalysis 
=> 
slowing or
halting 
enzymatic reactions.
Many drugs 
are 
=>
 
reversible
 enzyme inhibitors
.
They have their physiological effect by 
=> 
decreasing
=> the activity of a specific enzyme.
 For example,
 aspirin 
(
acetylsalicylate
) 
=> inhibits 
the
enzyme that catalyzes the first step in the synthesis of
prostaglandins
 => compounds involved in many
processes => including some that produce pain.
 
Concentration
 
of inhibitor 
needed => to 
inhibit
enzyme => depends on 
how tightly inhibitor
binds 
to the enzyme
.
 
Inhibition constant (Ki) 
is used to describe =>
how tightly an inhibitor binds to an enzyme.
 
  Types of Inhibitors
  There are 
two
 
broad classes 
of enzyme inhibitors:
• Irreversible
• Reversible
 
 
    Irreversible
irreversible inhibitors 
are those :
that 
bind covalently 
with enzyme or
destroy a functional group 
on an enzyme => that is
essential for enzyme’s activity
, or
that form => particularly 
stable
 
noncovalent association
.
 
Formation of a 
covalent link 
between => 
an irreversible
inhibitor
 and 
an enzyme 
is 
=> common
.
 
For example => reaction of 
chymotrypsin
 with
diisopropylfluorophosphate (DIFP) => 
irreversibly inhibits
enzyme by binding with 
Ser195
 in the 
active-site
 of
chymotrypsin
.
 
 
Diisopropylfluorophosphate as irreversible inhibitors of chymotrypsin
 
     
Reversible
This type of inhibition involves 
=>
 
equilibrium
between 
enzyme and inhibitor => 
equilibrium
constant 
(ki) => 
being the 
measure of affinity 
of the
inhibitor for the enzyme.
This inhibition is further 
classified into 
three
categories:
Competitive
Uncompetitive
Noncompetitive
.
 
     
Competitive Inhibition
Competitive inhibitors bind 
only
 to
 => free enzyme
and to the 
same site 
as the substrate.
Competitive inhibitors are => 
molecules
 that usually
look like the substrate 
but 
can’t undergo the reaction
.
At an 
infinite concentration 
of the substrate =>
competitive inhibitor 
cannot bind to the enzyme 
since
=> substrate concentration is high enough that => there
is virtually 
no free enzyme present
.
 
 
 
Since competitive inhibitors have => 
no effect on
the velocity 
at saturating (Vmax) concentrations
of the substrate => intercepts of the double
reciprocal plots (1/Vmax) at all the different
inhibitor concentrations are 
=> the same
.
The lines at different inhibitor concentrations =>
must all intersect 
on the y axis at the same
1/Vmax.
 
 
At 
low concentrations of substrate 
([S] << Km) =>
enzyme is predominantly in the 
E form
.
 
competitive inhibitor 
can 
combine with E 
=> so the
presence of the 
inhibitor => 
decreases => the
velocity 
when => 
substrate concentration is low
.
 
Competitive Inhibition
 
Under competitive inhibition
Vmax remains unchanged ; Km increases
 
Under competitive inhibition
Vmax remains unchanged ; Km increases
Example :
 
 
 
Malonate 
 is a 
competitive inhibitor 
of =>
succinate  dehydrogenase .
The enzyme 
uses
 
succinate as its
substrate 
but
 
inhibited
 
by malonate =>
which is 
structurally similar  
to succinate
and => 
differs
 in having => one rather
than two 
methylene  groups
.
 
     
Uncompetitive Inhibition
 
If 
inhibitor
 combines only => 
with ES 
(and not E) =>
inhibitor exerts its effect only at 
=> 
high concentrations
of substrate 
at which => there is lots of 
ES
 around.
 
This means that the 
increasing substrate 
concentration
(S) => 
doesn’t prevent => 
binding of the inhibitor
.
 
Interestingly Km value is consistently smaller than
Km value of the uninhibited reaction => which
implies that => 
S is more effectively bound to the
enzyme in the presence of    the    inhibitor.
 
The sequence of this type of reaction is
 
 
 
This type of inhibition is often observed for enzymes =>
that catalyze the 
reaction between 
two substrates
.
Often an inhibitor that is => 
competitive against one 
of the
substrates is found to give 
=> uncompetitive inhibition
 =>
when the other substrate is varied.
 
The inhibitor does combine at 
active site 
but => 
does not
prevent => binding
 of one of the substrates (and vice
versa).
 
Uncompetitive Inhibition
 
In this type of inhibition => 
Vmax as well as Km both are decreased
 
Non-competitive Inhibition
Compounds that 
reversibly
 bind 
with 
either the enzyme 
or the
enzyme substrate complex 
are designed as => 
noncompetitive
inhibitors
 and the following reaction describe these events.
 
 
 
Non competitive Inhibition
 
Noncompetitive inhibition
 therefore differs from competitive
inhibition in that => 
inhibitor
 can combine with
 ES
, and 
S
 can
combine with 
EI
 to form => in both instances 
EIS
.
 
This type of inhibition is 
not completely reversed 
by => 
high
substrate concentration 
=> since 
closed sequence 
will occur =>
regardless of the substrate concentration.
 
Since 
inhibitor 
binding site 
is 
not identical to
 
nor does it
modify the active site directly 
=> 
Km is not altered 
but 
Vmax
is decreased
.
 
For example => amino acid
 alanine 
noncompetitively
inhibits => 
enzyme 
pyruvate kinase
.
 
Alanine is one product of => a series of enzyme-
catalyzed reactions => first step of which is catalyzed by
pyruvate kinase
.
 
 
 
 
THANKS
Slide Note
Embed
Share

Enzyme inhibition plays a crucial role in pharmacology and biochemistry by regulating enzymatic reactions. Inhibitors can be reversible or irreversible, affecting enzyme activity differently. Competitive, uncompetitive, and noncompetitive inhibition types are explained along with examples like diisopropylfluorophosphate as an irreversible inhibitor of chymotrypsin. The concept of inhibition constant (Ki) is highlighted, illustrating how inhibitors bind to enzymes. Understanding these mechanisms is vital for drug design and understanding biological processes.


Uploaded on Aug 13, 2024 | 0 Views


Download Presentation

Please find below an Image/Link to download the presentation.

The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author. Download presentation by click this link. If you encounter any issues during the download, it is possible that the publisher has removed the file from their server.

E N D

Presentation Transcript


  1. BIOCHEMISTY Course No.-DTC-111, Credit Hours 2 (1+1) ENZYME INHIBITION BINITA RANI ASSOCIATE PROFESSOR (DAIRY CHEMISTRY) FACULTY OF DAIRY TECHNOLOGY S.G.I.D.T., BVC CAMPUS, P.O.- BVC, DIST.-PATNA-800014

  2. Inhibitors are molecules that => resemble the substrate(s) or product(s) and bind to => active site => thus => they interfere with catalysis => slowing or halting enzymatic reactions. Many drugs are => reversible enzyme inhibitors. They have their physiological effect by => decreasing => the activity of a specific enzyme. For example, aspirin (acetylsalicylate) => inhibits the enzyme that catalyzes the first step in the synthesis of prostaglandins => compounds involved in many processes => including some that produce pain.

  3. Concentration of inhibitor needed => to inhibit enzyme => depends on how tightly inhibitor binds to the enzyme. Inhibition constant (Ki) is used to describe => how tightly an inhibitor binds to an enzyme. Types of Inhibitors There are two broad classes of enzyme inhibitors: Irreversible Reversible

  4. Irreversible irreversible inhibitors are those : that bind covalently with enzyme or destroy a functional group on an enzyme => that is essential for enzyme s activity, or that form => particularly stable noncovalent association. Formation of a covalent link between => an irreversible inhibitor and an enzyme is => common. For example => reaction of chymotrypsin with diisopropylfluorophosphate (DIFP) => irreversibly inhibits enzyme by binding with Ser195 in the active-site of chymotrypsin.

  5. Diisopropylfluorophosphate as irreversible inhibitors of chymotrypsin

  6. Reversible This type of inhibition involves => equilibrium between enzyme and inhibitor => equilibrium constant (ki) => being the measure of affinity of the inhibitor for the enzyme. This inhibition is further classified into three categories: Competitive Uncompetitive Noncompetitive.

  7. Competitive Inhibition Competitive inhibitors bind only to => free enzyme and to the same site as the substrate. Competitive inhibitors are => molecules that usually look like the substrate but can t undergo the reaction. At an infinite concentration of the substrate => competitive inhibitor cannot bind to the enzyme since => substrate concentration is high enough that => there is virtually no free enzyme present.

  8. Since competitive inhibitors have => no effect on the velocity at saturating (Vmax) concentrations of the substrate => intercepts of the double reciprocal plots (1/Vmax) at all the different inhibitor concentrations are => the same. The lines at different inhibitor concentrations => must all intersect on the y axis at the same 1/Vmax.

  9. At low concentrations of substrate ([S] << Km) => enzyme is predominantly in the E form. competitive inhibitor can combine with E => so the presence of the inhibitor => decreases => the velocity when => substrate concentration is low.

  10. Competitive Inhibition Under competitive inhibition Vmax remains unchanged ; Km increases

  11. Under competitive inhibition Vmax remains unchanged ; Km increases Example : Malonate is a competitive inhibitor of => succinate dehydrogenase . The enzyme uses succinate as its substrate but inhibited by malonate => which is structurally similar to succinate and => differs in having => one rather than two methylene groups.

  12. Uncompetitive Inhibition If inhibitor combines only => with ES (and not E) => inhibitor exerts its effect only at => high concentrations of substrate at which => there is lots of ES around. This means that the increasing substrate concentration (S) => doesn t prevent => binding of the inhibitor.

  13. Interestingly Km value is consistently smaller than Km value of the uninhibited reaction => which implies that => S is more effectively bound to the enzyme in the presence of the inhibitor. The sequence of this type of reaction is

  14. This type of inhibition is often observed for enzymes => that catalyze the reaction between two substrates. Often an inhibitor that is => competitive against one of the substrates is found to give => uncompetitive inhibition => when the other substrate is varied. The inhibitor does combine at active site but => does not prevent => binding of one of the substrates (and vice versa).

  15. In this type of inhibition => Vmax as well as Km both are decreased Uncompetitive Inhibition

  16. Non-competitive Inhibition Compounds that reversibly bind with either the enzyme or the enzyme substrate complex are designed as => noncompetitive inhibitors and the following reaction describe these events. Non competitive Inhibition

  17. Noncompetitive inhibition therefore differs from competitive inhibition in that => inhibitor can combine with ES, and S can combine with EI to form => in both instances EIS. This type of inhibition is not completely reversed by => high substrate concentration => since closed sequence will occur => regardless of the substrate concentration. Since inhibitor binding site is not identical to nor does it modify the active site directly => Km is not altered but Vmax is decreased.

  18. For example => amino acid alanine noncompetitively inhibits => enzyme pyruvate kinase. Alanine is one product of => a series of enzyme- catalyzed reactions => first step of which is catalyzed by pyruvate kinase.

  19. THANKS

Related


More Related Content

giItT1WQy@!-/#giItT1WQy@!-/#giItT1WQy@!-/#giItT1WQy@!-/#giItT1WQy@!-/#